    /**
     * @class Ext.util.AbstractMixedCollection
     * @private
     */
    Ext.define('Ext.util.AbstractMixedCollection', {
        requires: ['Ext.util.Filter'],

        mixins: {
            observable: 'Ext.util.Observable'
        },

        /**
         * @property {Boolean} isMixedCollection
         * `true` in this class to identify an objact as an instantiated MixedCollection, or subclass thereof.
         */
        isMixedCollection: true,

        /**
         * @private Mutation counter which is incremented upon add and remove.
         */
        generation: 0,

        constructor: function(allowFunctions, keyFn) {
            var me = this;

            me.items = [];
            me.map = {};
            me.keys = [];
            me.length = 0;

                /**
                 * @event clear
                 * Fires when the collection is cleared.
                 */

                /**
                 * @event add
                 * Fires when an item is added to the collection.
                 * @param {Number} index The index at which the item was added.
                 * @param {Object} o The item added.
                 * @param {String} key The key associated with the added item.
                 */

                /**
                 * @event replace
                 * Fires when an item is replaced in the collection.
                 * @param {String} key he key associated with the new added.
                 * @param {Object} old The item being replaced.
                 * @param {Object} new The new item.
                 */
                /**
                 * @event remove
                 * Fires when an item is removed from the collection.
                 * @param {Object} o The item being removed.
                 * @param {String} key (optional) The key associated with the removed item.
                 */

            me.allowFunctions = allowFunctions === true;

            if (keyFn) {
                me.getKey = keyFn;
            }

            me.mixins.observable.constructor.call(me);
        },

        /**
         * @cfg {Boolean} allowFunctions Specify <code>true</code> if the {@link #addAll}
         * function should add function references to the collection. Defaults to
         * <code>false</code>.
         */
        allowFunctions : false,

        /**
         * Adds an item to the collection. Fires the {@link #event-add} event when complete.
         * @param {String} key <p>The key to associate with the item, or the new item.</p>
         * <p>If a {@link #getKey} implementation was specified for this MixedCollection,
         * or if the key of the stored items is in a property called <code><b>id</b></code>,
         * the MixedCollection will be able to <i>derive</i> the key for the new item.
         * In this case just pass the new item in this parameter.</p>
         * @param {Object} o The item to add.
         * @return {Object} The item added.
         */
        add : function(key, obj){
            var me = this,
                myObj = obj,
                myKey = key,
                old;

            if (arguments.length == 1) {
                myObj = myKey;
                myKey = me.getKey(myObj);
            }
            if (typeof myKey != 'undefined' && myKey !== null) {
                old = me.map[myKey];
                if (typeof old != 'undefined') {
                    return me.replace(myKey, myObj);
                }
                me.map[myKey] = myObj;
            }
            me.generation++;
            me.length++;
            me.items.push(myObj);
            me.keys.push(myKey);
            if (me.hasListeners.add) {
                me.fireEvent('add', me.length - 1, myObj, myKey);
            }
            return myObj;
        },

        /**
          * MixedCollection has a generic way to fetch keys if you implement getKey.  The default implementation
          * simply returns <b><code>item.id</code></b> but you can provide your own implementation
          * to return a different value as in the following examples:<pre><code>
    // normal way
    var mc = new Ext.util.MixedCollection();
    mc.add(someEl.dom.id, someEl);
    mc.add(otherEl.dom.id, otherEl);
    //and so on

    // using getKey
    var mc = new Ext.util.MixedCollection();
    mc.getKey = function(el){
       return el.dom.id;
    };
    mc.add(someEl);
    mc.add(otherEl);

    // or via the constructor
    var mc = new Ext.util.MixedCollection(false, function(el){
       return el.dom.id;
    });
    mc.add(someEl);
    mc.add(otherEl);
         * </code></pre>
         * @param {Object} item The item for which to find the key.
         * @return {Object} The key for the passed item.
         */
        getKey : function(o){
             return o.id;
        },

        /**
         * Replaces an item in the collection. Fires the {@link #event-replace} event when complete.
         * @param {String} key <p>The key associated with the item to replace, or the replacement item.</p>
         * <p>If you supplied a {@link #getKey} implementation for this MixedCollection, or if the key
         * of your stored items is in a property called <code><b>id</b></code>, then the MixedCollection
         * will be able to <i>derive</i> the key of the replacement item. If you want to replace an item
         * with one having the same key value, then just pass the replacement item in this parameter.</p>
         * @param o {Object} o (optional) If the first parameter passed was a key, the item to associate
         * with that key.
         * @return {Object}  The new item.
         */
        replace : function(key, o){
            var me = this,
                old,
                index;

            if (arguments.length == 1) {
                o = arguments[0];
                key = me.getKey(o);
            }
            old = me.map[key];
            if (typeof key == 'undefined' || key === null || typeof old == 'undefined') {
                 return me.add(key, o);
            }
            me.generation++;
            index = me.indexOfKey(key);
            me.items[index] = o;
            me.map[key] = o;
            if (me.hasListeners.replace) {
                me.fireEvent('replace', key, old, o);
            }
            return o;
        },

        /**
         * Adds all elements of an Array or an Object to the collection.
         * @param {Object/Array} objs An Object containing properties which will be added
         * to the collection, or an Array of values, each of which are added to the collection.
         * Functions references will be added to the collection if <code>{@link #allowFunctions}</code>
         * has been set to <code>true</code>.
         */
        addAll : function(objs){
            var me = this,
                i = 0,
                args,
                len,
                key;

            if (arguments.length > 1 || Ext.isArray(objs)) {
                args = arguments.length > 1 ? arguments : objs;
                for (len = args.length; i < len; i++) {
                    me.add(args[i]);
                }
            } else {
                for (key in objs) {
                    if (objs.hasOwnProperty(key)) {
                        if (me.allowFunctions || typeof objs[key] != 'function') {
                            me.add(key, objs[key]);
                        }
                    }
                }
            }
        },

        /**
         * Executes the specified function once for every item in the collection, passing the following arguments:
         * <div class="mdetail-params"><ul>
         * <li><b>item</b> : Mixed<p class="sub-desc">The collection item</p></li>
         * <li><b>index</b> : Number<p class="sub-desc">The item's index</p></li>
         * <li><b>length</b> : Number<p class="sub-desc">The total number of items in the collection</p></li>
         * </ul></div>
         * The function should return a boolean value. Returning false from the function will stop the iteration.
         * @param {Function} fn The function to execute for each item.
         * @param {Object} scope (optional) The scope (<code>this</code> reference) in which the function is executed. Defaults to the current item in the iteration.
         */
        each : function(fn, scope){
            var items = [].concat(this.items), // each safe for removal
                i = 0,
                len = items.length,
                item;

            for (; i < len; i++) {
                item = items[i];
                if (fn.call(scope || item, item, i, len) === false) {
                    break;
                }
            }
        },

        /**
         * Executes the specified function once for every key in the collection, passing each
         * key, and its associated item as the first two parameters.
         * @param {Function} fn The function to execute for each item.
         * @param {Object} scope (optional) The scope (<code>this</code> reference) in which the function is executed. Defaults to the browser window.
         */
        eachKey : function(fn, scope){
            var keys = this.keys,
                items = this.items,
                i = 0,
                len = keys.length;

            for (; i < len; i++) {
                fn.call(scope || window, keys[i], items[i], i, len);
            }
        },

        /**
         * Returns the first item in the collection which elicits a true return value from the
         * passed selection function.
         * @param {Function} fn The selection function to execute for each item.
         * @param {Object} scope (optional) The scope (<code>this</code> reference) in which the function is executed. Defaults to the browser window.
         * @return {Object} The first item in the collection which returned true from the selection function, or null if none was found
         */
        findBy : function(fn, scope) {
            var keys = this.keys,
                items = this.items,
                i = 0,
                len = items.length;

            for (; i < len; i++) {
                if (fn.call(scope || window, items[i], keys[i])) {
                    return items[i];
                }
            }
            return null;
        },

        //<deprecated since="0.99">
        find : function() {
            if (Ext.isDefined(Ext.global.console)) {
                Ext.global.console.warn('Ext.util.MixedCollection: find has been deprecated. Use findBy instead.');
            }
            return this.findBy.apply(this, arguments);
        },
        //</deprecated>

        /**
         * Inserts an item at the specified index in the collection. Fires the {@link #event-add} event when complete.
         * @param {Number} index The index to insert the item at.
         * @param {String} key The key to associate with the new item, or the item itself.
         * @param {Object} o (optional) If the second parameter was a key, the new item.
         * @return {Object} The item inserted.
         */
        insert : function(index, key, obj){
            var me = this,
                myKey = key,
                myObj = obj;

            if (arguments.length == 2) {
                myObj = myKey;
                myKey = me.getKey(myObj);
            }
            if (me.containsKey(myKey)) {
                me.suspendEvents();
                me.removeAtKey(myKey);
                me.resumeEvents();
            }
            if (index >= me.length) {
                return me.add(myKey, myObj);
            }
            me.generation++;
            me.length++;
            Ext.Array.splice(me.items, index, 0, myObj);
            if (typeof myKey != 'undefined' && myKey !== null) {
                me.map[myKey] = myObj;
            }
            Ext.Array.splice(me.keys, index, 0, myKey);
            if (me.hasListeners.add) {
                me.fireEvent('add', index, myObj, myKey);
            }
            return myObj;
        },

        /**
         * Remove an item from the collection.
         * @param {Object} o The item to remove.
         * @return {Object} The item removed or false if no item was removed.
         */
        remove : function(o) {
            this.generation++;
            return this.removeAt(this.indexOf(o));
        },

        /**
         * Remove all items in the passed array from the collection.
         * @param {Array} items An array of items to be removed.
         * @return {Ext.util.MixedCollection} this object
         */
        removeAll : function(items) {
            items = [].concat(items);
            var i, iLen = items.length;
            for (i = 0; i < iLen; i++) {
                this.remove(items[i]);
            }

            return this;
        },

        /**
         * Remove an item from a specified index in the collection. Fires the {@link #event-remove} event when complete.
         * @param {Number} index The index within the collection of the item to remove.
         * @return {Object} The item removed or false if no item was removed.
         */
        removeAt : function(index) {
            var me = this,
                o,
                key;

            if (index < me.length && index >= 0) {
                me.length--;
                o = me.items[index];
                Ext.Array.erase(me.items, index, 1);
                key = me.keys[index];
                if (typeof key != 'undefined') {
                    delete me.map[key];
                }
                Ext.Array.erase(me.keys, index, 1);
                if (me.hasListeners.remove) {
                    me.fireEvent('remove', o, key);
                }
                me.generation++;
                return o;
            }
            return false;
        },

        /**
         * Removed an item associated with the passed key fom the collection.
         * @param {String} key The key of the item to remove.
         * @return {Object} The item removed or false if no item was removed.
         */
        removeAtKey : function(key){
            return this.removeAt(this.indexOfKey(key));
        },

        /**
         * Returns the number of items in the collection.
         * @return {Number} the number of items in the collection.
         */
        getCount : function(){
            return this.length;
        },

        /**
         * Returns index within the collection of the passed Object.
         * @param {Object} o The item to find the index of.
         * @return {Number} index of the item. Returns -1 if not found.
         */
        indexOf : function(o){
            return Ext.Array.indexOf(this.items, o);
        },

        /**
         * Returns index within the collection of the passed key.
         * @param {String} key The key to find the index of.
         * @return {Number} index of the key.
         */
        indexOfKey : function(key){
            return Ext.Array.indexOf(this.keys, key);
        },

        /**
         * Returns the item associated with the passed key OR index.
         * Key has priority over index.  This is the equivalent
         * of calling {@link #getByKey} first, then if nothing matched calling {@link #getAt}.
         * @param {String/Number} key The key or index of the item.
         * @return {Object} If the item is found, returns the item.  If the item was not found, returns <code>undefined</code>.
         * If an item was found, but is a Class, returns <code>null</code>.
         */
        get : function(key) {
            var me = this,
                mk = me.map[key],
                item = mk !== undefined ? mk : (typeof key == 'number') ? me.items[key] : undefined;
            return typeof item != 'function' || me.allowFunctions ? item : null; // for prototype!
        },

        /**
         * Returns the item at the specified index.
         * @param {Number} index The index of the item.
         * @return {Object} The item at the specified index.
         */
        getAt : function(index) {
            return this.items[index];
        },

        /**
         * Returns the item associated with the passed key.
         * @param {String/Number} key The key of the item.
         * @return {Object} The item associated with the passed key.
         */
        getByKey : function(key) {
            return this.map[key];
        },

        /**
         * Returns true if the collection contains the passed Object as an item.
         * @param {Object} o  The Object to look for in the collection.
         * @return {Boolean} True if the collection contains the Object as an item.
         */
        contains : function(o){
            return typeof this.map[this.getKey(o)] != 'undefined';
        },

        /**
         * Returns true if the collection contains the passed Object as a key.
         * @param {String} key The key to look for in the collection.
         * @return {Boolean} True if the collection contains the Object as a key.
         */
        containsKey : function(key){
            return typeof this.map[key] != 'undefined';
        },

        /**
         * Removes all items from the collection.  Fires the {@link #event-clear} event when complete.
         */
        clear : function(){
            var me = this;

            me.length = 0;
            me.items = [];
            me.keys = [];
            me.map = {};
            me.generation++;
            if (me.hasListeners.clear) {
                me.fireEvent('clear');
            }
        },

        /**
         * Returns the first item in the collection.
         * @return {Object} the first item in the collection..
         */
        first : function() {
            return this.items[0];
        },

        /**
         * Returns the last item in the collection.
         * @return {Object} the last item in the collection..
         */
        last : function() {
            return this.items[this.length - 1];
        },

        /**
         * Collects all of the values of the given property and returns their sum
         * @param {String} property The property to sum by
         * @param {String} [root] 'root' property to extract the first argument from. This is used mainly when
         * summing fields in records, where the fields are all stored inside the 'data' object
         * @param {Number} [start=0] The record index to start at
         * @param {Number} [end=-1] The record index to end at
         * @return {Number} The total
         */
        sum: function(property, root, start, end) {
            var values = this.extractValues(property, root),
                length = values.length,
                sum    = 0,
                i;

            start = start || 0;
            end   = (end || end === 0) ? end : length - 1;

            for (i = start; i <= end; i++) {
                sum += values[i];
            }

            return sum;
        },

        /**
         * Collects unique values of a particular property in this MixedCollection
         * @param {String} property The property to collect on
         * @param {String} root (optional) 'root' property to extract the first argument from. This is used mainly when
         * summing fields in records, where the fields are all stored inside the 'data' object
         * @param {Boolean} allowBlank (optional) Pass true to allow null, undefined or empty string values
         * @return {Array} The unique values
         */
        collect: function(property, root, allowNull) {
            var values = this.extractValues(property, root),
                length = values.length,
                hits   = {},
                unique = [],
                value, strValue, i;

            for (i = 0; i < length; i++) {
                value = values[i];
                strValue = String(value);

                if ((allowNull || !Ext.isEmpty(value)) && !hits[strValue]) {
                    hits[strValue] = true;
                    unique.push(value);
                }
            }

            return unique;
        },

        /**
         * @private
         * Extracts all of the given property values from the items in the MC. Mainly used as a supporting method for
         * functions like sum and collect.
         * @param {String} property The property to extract
         * @param {String} root (optional) 'root' property to extract the first argument from. This is used mainly when
         * extracting field data from Model instances, where the fields are stored inside the 'data' object
         * @return {Array} The extracted values
         */
        extractValues: function(property, root) {
            var values = this.items;

            if (root) {
                values = Ext.Array.pluck(values, root);
            }

            return Ext.Array.pluck(values, property);
        },

        /**
         * Returns a range of items in this collection
         * @param {Number} startIndex (optional) The starting index. Defaults to 0.
         * @param {Number} endIndex (optional) The ending index. Defaults to the last item.
         * @return {Array} An array of items
         */
        getRange : function(start, end){
            var me = this,
                items = me.items,
                range = [],
                i;

            if (items.length < 1) {
                return range;
            }

            start = start || 0;
            end = Math.min(typeof end == 'undefined' ? me.length - 1 : end, me.length - 1);
            if (start <= end) {
                for (i = start; i <= end; i++) {
                    range[range.length] = items[i];
                }
            } else {
                for (i = start; i >= end; i--) {
                    range[range.length] = items[i];
                }
            }
            return range;
        },

        /**
         * <p>Filters the objects in this collection by a set of {@link Ext.util.Filter Filter}s, or by a single
         * property/value pair with optional parameters for substring matching and case sensitivity. See
         * {@link Ext.util.Filter Filter} for an example of using Filter objects (preferred). Alternatively,
         * MixedCollection can be easily filtered by property like this:</p>
    <pre><code>
    //create a simple store with a few people defined
    var people = new Ext.util.MixedCollection();
    people.addAll([
        {id: 1, age: 25, name: 'Ed'},
        {id: 2, age: 24, name: 'Tommy'},
        {id: 3, age: 24, name: 'Arne'},
        {id: 4, age: 26, name: 'Aaron'}
    ]);

    //a new MixedCollection containing only the items where age == 24
    var middleAged = people.filter('age', 24);
    </code></pre>
         *
         *
         * @param {Ext.util.Filter[]/String} property A property on your objects, or an array of {@link Ext.util.Filter Filter} objects
         * @param {String/RegExp} value Either string that the property values
         * should start with or a RegExp to test against the property
         * @param {Boolean} [anyMatch=false] True to match any part of the string, not just the beginning
         * @param {Boolean} [caseSensitive=false] True for case sensitive comparison.
         * @return {Ext.util.MixedCollection} The new filtered collection
         */
        filter : function(property, value, anyMatch, caseSensitive) {
            var filters = [],
                filterFn;

            //support for the simple case of filtering by property/value
            if (Ext.isString(property)) {
                filters.push(new Ext.util.Filter({
                    property     : property,
                    value        : value,
                    anyMatch     : anyMatch,
                    caseSensitive: caseSensitive
                }));
            } else if (Ext.isArray(property) || property instanceof Ext.util.Filter) {
                filters = filters.concat(property);
            }

            //at this point we have an array of zero or more Ext.util.Filter objects to filter with,
            //so here we construct a function that combines these filters by ANDing them together
            filterFn = function(record) {
                var isMatch = true,
                    length = filters.length,
                    i,
                    filter,
                    fn,
                    scope;

                for (i = 0; i < length; i++) {
                    filter = filters[i];
                    fn     = filter.filterFn;
                    scope  = filter.scope;

                    isMatch = isMatch && fn.call(scope, record);
                }

                return isMatch;
            };

            return this.filterBy(filterFn);
        },

        /**
         * Filter by a function. Returns a <i>new</i> collection that has been filtered.
         * The passed function will be called with each object in the collection.
         * If the function returns true, the value is included otherwise it is filtered.
         * @param {Function} fn The function to be called, it will receive the args o (the object), k (the key)
         * @param {Object} scope (optional) The scope (<code>this</code> reference) in which the function is executed. Defaults to this MixedCollection.
         * @return {Ext.util.MixedCollection} The new filtered collection
         */
        filterBy : function(fn, scope) {
            var me = this,
                newMC  = new this.self(),
                keys   = me.keys,
                items  = me.items,
                length = items.length,
                i;

            newMC.getKey = me.getKey;

            for (i = 0; i < length; i++) {
                if (fn.call(scope || me, items[i], keys[i])) {
                    newMC.add(keys[i], items[i]);
                }
            }

            return newMC;
        },

        /**
         * Finds the index of the first matching object in this collection by a specific property/value.
         * @param {String} property The name of a property on your objects.
         * @param {String/RegExp} value A string that the property values
         * should start with or a RegExp to test against the property.
         * @param {Number} [start=0] The index to start searching at.
         * @param {Boolean} [anyMatch=false] True to match any part of the string, not just the beginning.
         * @param {Boolean} [caseSensitive=false] True for case sensitive comparison.
         * @return {Number} The matched index or -1
         */
        findIndex : function(property, value, start, anyMatch, caseSensitive){
            if(Ext.isEmpty(value, false)){
                return -1;
            }
            value = this.createValueMatcher(value, anyMatch, caseSensitive);
            return this.findIndexBy(function(o){
                return o && value.test(o[property]);
            }, null, start);
        },

        /**
         * Find the index of the first matching object in this collection by a function.
         * If the function returns <i>true</i> it is considered a match.
         * @param {Function} fn The function to be called, it will receive the args o (the object), k (the key).
         * @param {Object} [scope] The scope (<code>this</code> reference) in which the function is executed. Defaults to this MixedCollection.
         * @param {Number} [start=0] The index to start searching at.
         * @return {Number} The matched index or -1
         */
        findIndexBy : function(fn, scope, start){
            var me = this,
                keys = me.keys,
                items = me.items,
                i = start || 0,
                len = items.length;

            for (; i < len; i++) {
                if (fn.call(scope || me, items[i], keys[i])) {
                    return i;
                }
            }
            return -1;
        },

        /**
         * Returns a regular expression based on the given value and matching options. This is used internally for finding and filtering,
         * and by Ext.data.Store#filter
         * @private
         * @param {String} value The value to create the regex for. This is escaped using Ext.escapeRe
         * @param {Boolean} anyMatch True to allow any match - no regex start/end line anchors will be added. Defaults to false
         * @param {Boolean} caseSensitive True to make the regex case sensitive (adds 'i' switch to regex). Defaults to false.
         * @param {Boolean} exactMatch True to force exact match (^ and $ characters added to the regex). Defaults to false. Ignored if anyMatch is true.
         */
        createValueMatcher : function(value, anyMatch, caseSensitive, exactMatch) {
            if (!value.exec) { // not a regex
                var er = Ext.String.escapeRegex;
                value = String(value);

                if (anyMatch === true) {
                    value = er(value);
                } else {
                    value = '^' + er(value);
                    if (exactMatch === true) {
                        value += '$';
                    }
                }
                value = new RegExp(value, caseSensitive ? '' : 'i');
            }
            return value;
        },

        /**
         * Creates a shallow copy of this collection
         * @return {Ext.util.MixedCollection}
         */
        clone : function() {
            var me = this,
                copy = new this.self(),
                keys = me.keys,
                items = me.items,
                i = 0,
                len = items.length;

            for(; i < len; i++){
                copy.add(keys[i], items[i]);
            }
            copy.getKey = me.getKey;
            return copy;
        }
    });